1. Field of the Invention
The present invention relates to an optical disk reproducing system, and especially to a control apparatus and method for controlling the velocity of a spindle motor in an optical disk system.
2. Description of the Related Art
An optical disk reproducing system, such as a compact disk player (CDP) or a digital versatile disk player (DVDP), conventionally uses a frame synchronous signal to control the velocity of a spindle motor when playback of a track recorded on an optical disk is commenced, a track jump occurs, or a spindle servo system is unstable. When a spindle servo is unlocked, a conventional spindle motor velocity control apparatus of the optical disk reproducing system operates at a constant linear velocity. The control apparatus detects the length of the frame synchronous signal and uses the length of the frame synchronous signal to make the spindle servo stable. For example, the conventional spindle motor velocity control apparatus of a CDP controls the velocity of the spindle motor based on whether the pulse width of an eight-to-fourteen modulation (EFM) signal is narrower or wider than 11T, where T, the period of a main clock signal (PLCK), is about 231 nanoseconds.
The conventional control apparatus for controlling the velocity of the spindle motor described above can be useful when the disk is normal, that is, there are no abnormalities or imperfections on its surface. However, the conventional control apparatus regards the pattern of the frame synchronous signal as much wider than 11T when some deficiencies such as a scratch or a fingerprint exist on the disk. Thus, in this case, the conventional control apparatus increases the velocity of the spindle motor, which can result in an overrun of the spindle motor.
Furthermore, a slice circuit of the optical disk reproducing system converts a radio frequency (RF) signal to binary data of a CMOS (Complementary Metal Oxide Semiconductor) logic level. Also, the above-described conventional control apparatus for controlling the velocity of the spindle motor can cause the overrun of the spindle motor to occur even when an error occurs in the frame synchronous signal because of an inadequate reference voltage.
It is an object of the present invention to provide a control apparatus and method for controlling the velocity of a spindle motor in an optical disk reproducing system to prevent backward or forward overrun of the spindle motor.
The invention includes a widest signal detector for detecting the widest pulse width of an EFM signal and/or EFM-PLUS signal in response to a main clock signal. The widest signal detector generates first status signals representing the status of the detected pulse width in response to a frame clock signal which is divided by a first predetermined number j. A narrowest signal detector generates second status signals representing the status of the narrowest pulse width of the first status signals in response to the frame clock signal divided by a second predetermined number k, where k is greater than j. An overrun controller performs up-counting or down-counting or holds a previously counted result corresponding to the frame clock signal divided by the second predetermined number and the second status signals. The overrun controller compares the currently counted result with overrun upper limit and lower limit values, and generates first and second flag signals to brake the rotation of the spindle motor according to the compared result.
In one embodiment, the control apparatus of the invention also includes a pulse width modulation signal generator which generates a velocity control signal with logic levels corresponding to logic levels of the second status signals and transmits the velocity control signal to the spindle motor. The velocity of the spindle motor is controlled, i.e., increased, decreased or held constant, according to the velocity control signal.
In one embodiment, the overrun controller of the invention includes an enable signal generator for generating upward and downward enable signals with logic levels determined by the second status signals. A counter performs up-counting, down-counting and holding constant the previously counted result in response to the upward and downward enable signals during a predetermined period of the frame clock signal divided by the second predetermined number. A flag signal generator compares the currently counted result with the overrun upper limit and lower limit values and generates the first and second flag signals according to the compared result. In one particular embodiment, the flag signal generator includes a first comparator for comparing the currently counted result with the overrun upper limit value and generates the compared result as the first flag signal. A second comparator compares the currently counted result with the overrun lower limit value and generates the compared result as the second flag signal.
In accordance with the method of the invention, at each first predetermined frame interval, the widest pulse width of an EFM signal and/or EFM-PLUS signal is detected. At each second predetermined frame interval wider than the first predetermined frame interval, the narrowest pulse width of the pulse widths detected in the previous step is detected. A previously counted result is up-counted, down-counted or held constant during the second predetermined frame interval according to the status of the detected narrowest pulse width. Braking is applied to the rotation of the spindle motor according to whether the currently counted result is smaller than an overrun upper limit value and greater than an overrun lower limit value.
In one embodiment of the method of the invention, the velocity of the spindle is controlled according to the status of the detected narrowest pulse width.
In accordance with an embodiment of the method of the invention, it is determined whether the detected narrowest pulse width is greater than a predetermined pulse width. If so, then the counted result is up-counted during the second predetermined frame interval. If the detected narrowest pulse width is smaller than the predetermined pulse width, then the counted result is down-counted during the second predetermined frame interval. If the detected narrowest pulse width is the same as the predetermined pulse width, then the counted result is held constant during the second predetermined frame interval. The currently counted result is compared to the upper limit value and the lower limit value. If the currently counted result is between the upper and lower limit values, then it is determined that no overrun has occurred. Rotation of the spindle is stopped if the currently counted result is greater than the overrun upper limit value or smaller than the overrun lower limit value.
The control apparatus and method for controlling the velocity of the spindle motor according to the present invention can stabilize the spindle motor using the status of the pulse width of the EFM signal and/or EFM-PLUS signal when a forward or backward overrun occurs because of flaws on the disk surface.